The present invention pertains to data transmission between a microprocessor and peripheral devices and more particularly to the elimination of timing skew in a multiplexed address and data bus between a microprocessor and remotely located peripheral devices.
Several current microprocessors, including the Intel 8086 for example, incorporate a multiplexed address and data bus to reduce the number of terminal pins required for the integrated circuit. Typically, this bus is de-multiplexed locally and the address and data buses are sent separately to the peripheral devices. A considerable savings in signal leads can be realized in large telephone systems by extending these multiplexed buses directly to the remotely located peripheral devices. Several additional control leads are required at the remote location of the peripheral device to de-multiplex this bus, but 36 signal leads can be saved in a 16-bit system, for example.
Cables to connect the microprocessor to the peripheral devices can range in length up to one hundred feet long. Signals propogating along a one hundred foot length of cable tend to become skewed, that is they arrive at their destination at different times. This skew cannot be tolerated by the high speed microprocessors such as the Intel 8086.
Conventional approaches add many wait states in the microprocessor cycle to accommodate this propagation delay. This means the microprocessor is locked onto or awaiting the transmission from the peripheral device. This is an undesirable situation since valuable processor real-time is lost.
Accordingly, it is the object of the present invention to provide for the transmission of a multiplexed address and data bus to remotely located peripheral devices in an efficient real-time manner.
It is a further object of the present invention to provide functions mentioned above in a cost effective manner.
It is another object of the present invention to provide a circuit which is small in the number of different types of components employed.
It is a yet another object of the present invention to provide a circuit which is expandable for longer cabling lengths.